Re: [PATCH v2 0/4] timer: Improve itimers scalability

Ingo Molnar
2015-10-15T08:47:11Z

* Jason Low <jason.low2@hp.com> wrote:

> While running a database workload on a 16 socket machine, there were
> scalability issues related to itimers. The following link contains a
> more detailed summary of the issues at the application level.
>
> https://lkml.org/lkml/2015/8/26/737
>
> Commit 1018016c706f addressed the issue with the thread_group_cputimer
> spinlock taking up a significant portion of total run time.
> This patch series addresses the secondary issue where a lot of time is
> spent trying to acquire the sighand lock. It was found in some cases
> that 200+ threads were simultaneously contending for the same sighand
> lock, reducing throughput by more than 30%.
>
> With this patch set (along with commit 1018016c706f mentioned above),
> the performance hit of itimers almost completely goes away on the
> 16 socket system.
>
> Jason Low (4):
> timer: Optimize fastpath_timer_check()
> timer: Check thread timers only when there are active thread timers
> timer: Convert cputimer->running to bool
> timer: Reduce unnecessary sighand lock contention
>
> include/linux/init_task.h | 3 +-
> include/linux/sched.h | 9 ++++--
> kernel/fork.c | 2 +-
> kernel/time/posix-cpu-timers.c | 63 ++++++++++++++++++++++++++++-----------
> 4 files changed, 54 insertions(+), 23 deletions(-)

Is there some itimers benchmark that can be used to measure the effects of these
changes?

Thanks,

Ingo